ABSTRACT The illicit use of prescription stimulants (e.g., Adderall, Ritalin) is a form of substance use prevalent among college students in the United States. One behavior driving the illicit use of prescription stimulants (IUPS) is prescription stimulant diversion (e.g., sharing and/or selling medication). In response, a growing number of states and campuses have passed policies intended to decrease both diversion and IUPS. Our preliminary studies show that not all students who are approached to divert do so, and not all students who initiate IUPS maintain this behavior. However, we do not know if students are being influenced by these policies, or if other deterrents to diversion and IUPS are more influential. Our goal, therefore, is to understand factors that may deter both diversion and IUPS from the perspective of students who have initiated these behaviors. Attainment of this goal could be applied to reduce morbidity and mortality related to IUPS. The proposed study, therefore, aligns with NIH's mission of seeking and applying fundamental knowledge about behavior to promote health. The objective of this three-year R15 study is to provide a more comprehensive understanding of IUPS by achieving the following: AIM1A: Explore students' knowledge about existing prescription stimulant diversion policy and non-policy deterrents. AIM1B: Explore students' knowledge about existing IUPS policy and non-policy deterrents. AIM2A: Describe students' attitudes towards existing and potential prescription stimulant diversion policy and non-policy deterrents. AIM2B: Describe students' attitudes towards existing and potential IUPS policy and non-policy deterrents. The study will be set at one ethnically-diverse campus in southern California. Survey data from a representative sample of the student population showed this campus has both diverters and non-diverters, and students who currently and formerly engaged in IUPS. For our proposed study, a maximum of 32 students with a history of prescription stimulant diversion and/or IUPS will be recruited to participate in semi-structured interviews led by student research assistants. The focus of the interviews will be to discuss knowledge about and attitudes towards policy and non-policy related deterrents to prescription stimulant diversion and IUPS. Our proposed study is hypothesis-generating in nature, and we will analyze the qualitative data inductively using a thematic analysis procedure